Introduction: Is There Life On Mars?

In 1976 two spacecraft arrived at Mars, each of which included a lander equipped with a life-detection package: after at least a century of debate and speculation we were finally going to learn if life existed on this distant world that had for so long loomed large in the human consciousness, our first real opportunity to discover whether or not the Earth was alone in originating life.

Soon after the arrival of the Viking 1 spacecraft at Mars and prior to the release of its Lander down to the planet's surface, James Burke hosted a TV documentary, aired in the UK, that discussed the spacecraft and its mission, in particular the search for life and I will be drawing on a recording of this in the following discussion. In Burke's words: "If Viking finds that there is life present at the landing site it will considerably alter our thinking as to whether or not we are alone in the galaxy."

As to whether or not the Viking Landers' detected life remains, however, an open question for whilst the general scientific consensus has for decades now been that life was not found, there is today a small, but growing number of scientists who, using new evidence and analytical methodologies, consider that one experiment, the labelled release experiment, did find life on Mars (see 'Papers').

I want us now to take a step back, however, to ask why we would expect to find life beyond the Earth at all, let alone beyond our own solar system or on Mars. Why would we expect that the conditions necessary for a planet to generate life would exist universally rather than only locally?

The concept of the inevitability of life has been with us for some time. In 1954, the year after Stanley Miller's famous experiment on the origins of life and Crick & Watson's determination of the physical structure of DNA, biologist George Wald wrote that it was in the character of natural phenomena, "...to be repetitive, and hence given time, to be inevitable. This is by far our most significant conclusion - that life, as an orderly natural event on such a planet as ours, was inevitable. The same can be said of the whole of organic evolution. All of it lies within the order of nature, and apart from details, all of it was inevitable." Notably, Wald was also among the few scientists at this time to extend experimental results on the origins of life on Earth to other planets. Thus, he adds, "What it means to bring the origin of life within the realm of natural phenomena is to imply that in all these places [Earth-like planets] life probably exists - life as we know it... Wherever life is possible, given time, it should arise." The Urey-Miller experiment, that produced a variety of amino acids from a simulated reducing atmosphere - one rich in hydrogen - became highly influential and suggested that the origin of life was in some sense easy. Other scientists, however, have seen the origins of life to be more problematic.